Variants in the gene SCN1A encoding Nav1.1 α subunit have been associated with a spectrum of epilepsy disorders ranging from the relatively benign generalized epilepsy with febrile seizures plus (GEFS+) to the devastating disorder, severe myoclonic epilepsy of infancy (SMEI) (Escayg et al., 2000, 2001; Marini et al., 2009). The gene discussed is SCN1A; the disease is myoclonic epilepsy.